Two of NASA’s Space Telescopes Team Up to Spot Distant Brown Dwarf

Scaled somewhere between small stars and large planets, brown dwarfs are among the universe's most curious phenomena. Though they can be up to 80 times more massive than our solar system's giant, Jupiter, their cores are not robust enough to generate starlight through hydrogen-helium fusion. As a result, it can be challenging to detect these dim worlds, or "failed stars" as they are sometimes called, especially from great distances.

But sometimes, astronomers catch a lucky break with the help of gravitational microlensing, which is like a cosmic riff on a magnifying glass. The gravitational fields of massive objects distort the light of background objects around them, amplifying their light from our perspective on Earth, and that enables astronomers to study them more closely.

According to new research published this week in the Astrophysical Journal, NASA researchers used the effect to discover a brown dwarf located at the enormous distance of five kiloparsecs (16,300 light years) from our solar system.

This far-flung world, named OGLE-2015-BLG-1319, is estimated to be about 30 to 65 Jupiter masses, and orbits a K-type star in the Morgan–Keenan stellar classification system, meaning it's midway in mass between small M-type dwarf stars and G-type stars like the Sun. It was first detected by the Warsaw-based Optical Gravitational Lensing Experiment (OGLE), and confirmed with subsequent observations from NASA's Spitzer and Swift space telescopes.

Spotting such a faint object over a huge swath of space is a feat in itself, but the new find may be exceptional for another reason: Brown dwarfs very rarely orbit within three astronomical units of their host stars (one of these units represents the distance between the Earth and the Sun). This pattern is known as the "brown-dwarf desert" and OGLE-2015-BLG-1319 may be the only known exception, though further observations will be necessary to confirm that hunch.

"We want to understand how brown dwarfs form around stars, and why there is a gap in where they are found relative to their host stars," said Yossi Shvartzvald, a NASA postdoctoral fellow and lead author of the new study. "It's possible that the 'desert' is not as dry as we think."

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